Bile acids modulate reinstatement of cocaine conditioned place preference and accumbal dopamine dynamics without compromising appetitive learning.

Psychostimulants target the dopamine transporter (DAT) to elicit their psychomotor actions. Bile acids (BAs) can also bind to DAT and reduce behavioral responses to cocaine, suggesting a potential therapeutic application of BAs in psychostimulant use disorder. Here, we investigate the potential of BAs to decrease drug-primed reinstatement when administered during an abstinence phase. To do this, after successful development of cocaine-associated contextual place preference (cocaine CPP), cocaine administration was terminated, and animals treated with vehicle or obeticholic acid (OCA). When preference for the cocaine-associated context was extinguished, mice were challenged with a single priming dose of cocaine, and reinstatement of cocaine-associated contextual preference was measured. Animals treated with OCA demonstrate a significantly lower reinstatement for cocaine CPP. OCA also impairs the ability of cocaine to reduce the clearance rate of electrically stimulated dopamine release and diminishes the area under the curve (AUC) observed with amperometry. Furthermore, the AUC of the amperometric signal positively correlates with the reinstatement index. Using operant feeding devices, we demonstrate that OCA has no effect on contextual learning or motivation for natural rewards. These data highlight OCA as a potential therapeutic for cocaine use disorder.

Faulty Metabolism: A Potential Instigator of an Aggressive Phenotype in Cdk5-dependent Medullary Thyroid Carcinoma.

Mechanistic modeling of cancers such as Medullary Thyroid Carcinoma (MTC) to emulate patient-specific phenotypes is challenging. The discovery of potential diagnostic markers and druggable targets in MTC urgently requires clinically relevant animal models. Here we established orthotopic mouse models of MTC driven by aberrantly active Cdk5 using cell-specific promoters. Each of the two models elicits distinct growth differences that recapitulate the less or more aggressive forms of human tumors. The comparative mutational and transcriptomic landscape of tumors revealed significant alterations in mitotic cell cycle processes coupled with the slow-growing tumor phenotype. Conversely, perturbation in metabolic pathways emerged as critical for aggressive tumor growth. Moreover, an overlapping mutational profile was identified between mouse and human tumors. Gene prioritization revealed putative downstream effectors of Cdk5 which may contribute to the slow and aggressive growth in the mouse MTC models. In addition, Cdk5/p25 phosphorylation sites identified as biomarkers for Cdk5-driven neuroendocrine tumors (NETs) were detected in both slow and rapid onset models and were also histologically present in human MTC. Thus, this study directly relates mouse and human MTC models and uncovers vulnerable pathways potentially responsible for differential tumor growth rates. Functional validation of our findings may lead to better prediction of patient-specific personalized combinational therapies.

Syntaxin 1 Ser14 phosphorylation is required for nonvesicular dopamine release.

Amphetamine (AMPH) is a psychostimulant that is commonly abused. The stimulant properties of AMPH are associated with its ability to increase dopamine (DA) neurotransmission. This increase is promoted by nonvesicular DA release mediated by reversal of DA transporter (DAT) function. Syntaxin 1 (Stx1) is a SNARE protein that is phosphorylated at Ser14 by casein kinase II. We show that Stx1 phosphorylation is critical for AMPH-induced nonvesicular DA release and, in Drosophila melanogaster, regulates the expression of AMPH-induced preference and sexual motivation. Our molecular dynamics simulations of the DAT/Stx1 complex demonstrate that phosphorylation of these proteins is pivotal for DAT to dwell in a DA releasing state. This state is characterized by the breakdown of two key salt bridges within the DAT intracellular gate, causing the opening and hydration of the DAT intracellular vestibule, allowing DA to bind from the cytosol, a mechanism that we hypothesize underlies nonvesicular DA release.

Genetic impairment of succinate metabolism disrupts bioenergetic sensing in adrenal neuroendocrine cancer.

Metabolic dysfunction mutations can impair energy sensing and cause cancer. Loss of function of the mitochondrial tricarboxylic acid (TCA) cycle enzyme subunit succinate dehydrogenase B (SDHB) results in various forms of cancer typified by pheochromocytoma (PC). Here we delineate a signaling cascade where the loss of SDHB induces the Warburg effect, triggers dysregulation of [Ca2+]i, and aberrantly activates calpain and protein kinase Cdk5, through conversion of its cofactor from p35 to p25. Consequently, aberrant Cdk5 initiates a phospho-signaling cascade where GSK3 inhibition inactivates energy sensing by AMP kinase through dephosphorylation of the AMP kinase γ subunit, PRKAG2. Overexpression of p25-GFP in mouse adrenal chromaffin cells also elicits this phosphorylation signaling and causes PC. A potent Cdk5 inhibitor, MRT3-007, reverses this phospho-cascade, invoking a senescence-like phenotype. This therapeutic approach halted tumor progression in vivo. Thus, we reveal an important mechanistic feature of metabolic sensing and demonstrate that its dysregulation underlies tumor progression in PC and likely other cancers.

A retrospective observational research study to describe the real-world use of bosutinib in patients with chronic myeloid leukemia in the United Kingdom and the Netherlands.

OBJECTIVES: To describe the real-world effectiveness and safety of bosutinib in patients with chronic myeloid leukemia (CML). METHODS: This was a multi-center, retrospective, non-interventional chart review study conducted in 10 hospitals in the United Kingdom and the Netherlands. RESULTS: Eighty-seven patients were included. Bosutinib was the third-line tyrosine kinase inhibitor (TKI) in 33 (38%) and fourth-line in 44 (51%) patients. Median treatment duration was 15.6 months. Among 84 patients in chronic phase (CP) at baseline, 26 (31%) switched to bosutinib due to resistance and 57 (68%) due to intolerance to prior TKIs. Cumulative complete cytogenetic and major molecular response rates in CP patients were 67% and 55%, respectively. After a median follow-up of 21.5 months, nine (11%) patients in CP died; estimated overall survival rates at 1 and 2 years postbosutinib initiation were 95% and 91%, respectively. Overall, 33/87 (38%) patients discontinued bosutinib due to either lack of efficacy/disease progression (17%), adverse events (14%), death (2%), or other reasons (5%). Eighty-two (94%) patients experienced ≥1 adverse event possibly related to bosutinib, most commonly diarrhea (52%). CONCLUSIONS: Bosutinib used in routine clinical practice in heavily pretreated patients with CML is an effective treatment for patients in CP and is generally tolerable.

Bile Acids Gate Dopamine Transporter Mediated Currents.

Bile acids (BAs) are molecules derived from cholesterol that are involved in dietary fat absorption. New evidence supports an additional role for BAs as regulators of brain function. Sterols such as cholesterol interact with monoamine transporters, including the dopamine (DA) transporter (DAT) which plays a key role in DA neurotransmission and reward. This study explores the interactions of the BA, obeticholic acid (OCA), with DAT and characterizes the regulation of DAT activity via both electrophysiology and molecular modeling. We expressed murine DAT (mDAT) in Xenopus laevis oocytes and confirmed its functionality. Next, we showed that OCA promotes a DAT-mediated inward current that is Na+-dependent and not regulated by intracellular calcium. The current induced by OCA was transient in nature, returning to baseline in the continued presence of the BA. OCA also transiently blocked the DAT-mediated Li+-leak current, a feature that parallels DA action and indicates direct binding to the transporter in the absence of Na+. Interestingly, OCA did not alter DA affinity nor the ability of DA to promote a DAT-mediated inward current, suggesting that the interaction of OCA with the transporter is non-competitive, regarding DA. Docking simulations performed for investigating the molecular mechanism of OCA action on DAT activity revealed two potential binding sites. First, in the absence of DA, OCA binds DAT through interactions with D421, a residue normally involved in coordinating the binding of the Na+ ion to the Na2 binding site (Borre et al., J. Biol. Chem., 2014, 289, 25764-25773; Cheng and Bahar, Structure, 2015, 23, 2171-2181). Furthermore, we uncover a separate binding site for OCA on DAT, of equal potential functional impact, that is coordinated by the DAT residues R445 and D436. Binding to that site may stabilize the inward-facing (IF) open state by preventing the re-formation of the IF-gating salt bridges, R60-D436 and R445-E428, that are required for DA transport. This study suggests that BAs may represent novel pharmacological tools to regulate DAT function, and possibly, associated behaviors.

Cdk5 drives formation of heterogeneous pancreatic neuroendocrine tumors.

Pancreatic neuroendocrine tumors (PanNETs) are a heterogeneous population of neoplasms that arise from hormone-secreting islet cells of the pancreas and have increased markedly in incidence over the past four decades. Non-functional PanNETs, which occur more frequently than hormone-secreting tumors, are often not diagnosed until later stages of tumor development and have poorer prognoses. Development of successful therapeutics for PanNETs has been slow, partially due to a lack of diverse animal models for pre-clinical testing. Here, we report development of an inducible, conditional mouse model of PanNETs by using a bi-transgenic system for regulated expression of the aberrant activator of Cdk5, p25, specifically in ß-islet cells. This model produces a heterogeneous population of PanNETs that includes a subgroup of well-differentiated, non-functional tumors. Production of these tumors demonstrates the causative potential of aberrantly active Cdk5 for generation of PanNETs. Further, we show that human PanNETs express Cdk5 pathway components, are dependent on Cdk5 for growth, and share genetic and transcriptional overlap with the INS-p25OE model. The utility of this model is enhanced by the ability to form tumor-derived allografts. This new model of PanNETs will facilitate molecular delineation of Cdk5-dependent PanNETs and the development of new targeted therapeutics.

Lipid management across Europe in the real-world setting: a rapid evidence review.

OBJECTIVE: To provide a contemporary overview of recent real-world lipid-lowering therapy (LLT) practices and outcomes in patients with hypercholesterolemia/dyslipidemia at high/very high risk of atherosclerotic cardiovascular disease in Europe. METHODS: A structured literature review of recent (July 2015-July 2020) real-world studies reporting lipid management and outcomes was conducted using a rapid evidence synthesis. Outcomes included patient characteristics, LLT treatment practices, adherence and low-density lipoprotein cholesterol (LDL-C) goal attainment. RESULTS: Fifty-three real-world observational studies in high/very high risk patients were selected after screening 5664 records (n = 50 national [sample size range 38-237,279] and n = 3 multinational studies [sample size range 6648-8456]). Mean age ranged from 33 to 77 years; hypertension, diabetes and obesity were commonly reported comorbidities. Statins were the most common LLT; patients without familial hypercholesterolemia (FH) mostly received high or moderate intensity statins/LLT, while patients with FH mostly received high intensity statins/LLT. The proportion of patients receiving ezetimibe was low overall (ezetimibe + statin use in those with and without familial hypercholesterolemia [FH] range 5%-59% and 1%-22%, respectively). Overall, the use of proprotein convertase subtilisin/kexin 9 inhibitor (PCSK9i) therapy was limited. Adherence to LLT therapies was defined variably and ranged from 46%-92%. LDL-C goal attainment was suboptimal, irrespective of LLT (overall range in goal attainment with oral LLT was 2%-73% [FH: 2%-23%] and with PCSK9i was 20%-65%). CONCLUSIONS: LDL-C control is suboptimal and the available LLT armamentarium, most importantly combination therapy, is being underutilized in high/very high risk patients leading to inadequate management of cardiovascular risk.

Psychomotor impairments and therapeutic implications revealed by a mutation associated with infantile Parkinsonism-Dystonia.

Parkinson disease (PD) is a progressive, neurodegenerative disorder affecting over 6.1 million people worldwide. Although the cause of PD remains unclear, studies of highly penetrant mutations identified in early-onset familial parkinsonism have contributed to our understanding of the molecular mechanisms underlying disease pathology. Dopamine (DA) transporter (DAT) deficiency syndrome (DTDS) is a distinct type of infantile parkinsonism-dystonia that shares key clinical features with PD, including motor deficits (progressive bradykinesia, tremor, hypomimia) and altered DA neurotransmission. Here, we define structural, functional, and behavioral consequences of a Cys substitution at R445 in human DAT (hDAT R445C), identified in a patient with DTDS. We found that this R445 substitution disrupts a phylogenetically conserved intracellular (IC) network of interactions that compromise the hDAT IC gate. This is demonstrated by both Rosetta molecular modeling and fine-grained simulations using hDAT R445C, as well as EPR analysis and X-ray crystallography of the bacterial homolog leucine transporter. Notably, the disruption of this IC network of interactions supported a channel-like intermediate of hDAT and compromised hDAT function. We demonstrate that Drosophila melanogaster expressing hDAT R445C show impaired hDAT activity, which is associated with DA dysfunction in isolated brains and with abnormal behaviors monitored at high-speed time resolution. We show that hDAT R445C Drosophila exhibit motor deficits, lack of motor coordination (i.e. flight coordination) and phenotypic heterogeneity in these behaviors that is typically associated with DTDS and PD. These behaviors are linked with altered dopaminergic signaling stemming from loss of DA neurons and decreased DA availability. We rescued flight coordination with chloroquine, a lysosomal inhibitor that enhanced DAT expression in a heterologous expression system. Together, these studies shed some light on how a DTDS-linked DAT mutation underlies DA dysfunction and, possibly, clinical phenotypes shared by DTDS and PD.

Routine management, healthcare resource use and patient and carer-reported outcomes of patients with transfusion-dependent ß-thalassaemia in the United Kingdom: A mixed methods observational study.

Objectives: We evaluated routine healthcare management, clinical status and patient- and carer-reported outcomes in UK paediatric and adult patients with transfusion-dependent ß-thalassaemia (TDT). Methods: A multi-centre, observational mixed-methodology study evaluated 165 patients (50% male; median age 24.1 [interquartile range (IQR)] 11.8-37.2] years) from nine UK centres. Results: Patients had a mean of 13.7 (standard deviation [SD] ±3.2) transfusion episodes/year (mean retrospective observation period 4.7 [±0.7] years). The median (IQR) for iron overload parameters at the last assessment during the observation period were: serum ferritin (n = 165) 1961.0 (1090.0-3003.0) µg/L (38% > 2500 µg/L); R2 liver iron (n = 119) 5.4 (2.9-11.6) mg/g (16% ≥15 mg/g); T2* cardiac iron (n = 132) 30.3 (22.0-37.1) ms (10% < 10 ms). All patients received ≥1 iron chelator during the observation period; 21% received combination therapy. Patients had a mean of 7.8 (±8.1) non-transfusion-related hospital attendances or admissions/year. Adult patients' mean EQ-5D utility score was 0.69 (±0.33; n = 94 [≥16 years]) and mean Transfusion-dependent quality of life score was 58.6 (±18.4; n = 94 [≥18 years]). For Work Productivity and Activity impairment, mean activity impairment for patients ≥18 years (n = 88) was 48% (±32%) and for carers (n = 29) was 28% (±23%). Conclusions: TDT presents significant burden on patients, carers and healthcare resources.

Anti-SSTR2 antibody-drug conjugate for neuroendocrine tumor therapy.

Neuroendocrine (NE) tumors include a diverse spectrum of hormone-secreting neoplasms that arise from the endocrine and nervous systems. Current chemo- and radio-therapies have marginal curative benefits. The goal of this study was to develop an innovative antibody-drug conjugate (ADC) to effectively treat NE tumors (NETs). First, we confirmed that somatostatin receptor 2 (SSTR2) is an ideal cancer cell surface target by analyzing 38 patient-derived NET tissues, 33 normal organs, and three NET cell lines. Then, we developed a new monoclonal antibody (mAb, IgG1, and kappa) to target two extracellular domains of SSTR2, which showed strong and specific surface binding to NETs. The ADC was constructed by conjugating the anti-SSTR2 mAb and antimitotic monomethyl auristatin E. In vitro evaluations indicated that the ADC can effectively bind, internalize, release payload, and kill NET cells. Finally, the ADC was evaluated in vivo using a NET xenograft mouse model to assess cancer-specific targeting, tolerated dosage, pharmacokinetics, and antitumor efficacy. The anti-SSTR2 ADC exclusively targeted and killed NET cells with minimal toxicity and high stability in vivo. This study demonstrates that the anti-SSTR2 ADC has a high-therapeutic potential for NET therapy.

Phosphoprotein-based biomarkers as predictors for cancer therapy.

Disparities in cancer patient responses have prompted widespread searches to identify differences in sensitive vs. nonsensitive populations and form the basis of personalized medicine. This customized approach is dependent upon the development of pathway-specific therapeutics in conjunction with biomarkers that predict patient responses. Here, we show that Cdk5 drives growth in subgroups of patients with multiple types of neuroendocrine neoplasms. Phosphoproteomics and high throughput screening identified phosphorylation sites downstream of Cdk5. These phosphorylation events serve as biomarkers and effectively pinpoint Cdk5-driven tumors. Toward achieving targeted therapy, we demonstrate that mouse models of neuroendocrine cancer are responsive to selective Cdk5 inhibitors and biomimetic nanoparticles are effective vehicles for enhanced tumor targeting and reduction of drug toxicity. Finally, we show that biomarkers of Cdk5-dependent tumors effectively predict response to anti-Cdk5 therapy in patient-derived xenografts. Thus, a phosphoprotein-based diagnostic assay combined with Cdk5-targeted therapy is a rational treatment approach for neuroendocrine malignancies.

Review of metastatic colorectal cancer treatment pathways and early clinical experience of trifluridine/tipiracil in the UK named patient programme.

BACKGROUND: The standard first- and second- line chemotherapy backbone regimens for metastatic colorectal cancer (mCRC) are 5-fluorouracil (5-FU)/capecitabine-based with addition of irinotecan or oxaliplatin. Until recently, evidence for optimal sequencing post second-line was sparse. Trifluridine/tipiracil (indicated for mCRC and gastric cancer after standard chemotherapies) was made available to UK patients via a named patient programme (NPP) before receiving marketing authorisation in Europe in 2016, allowing characterisation of UK treatment pathways, and evaluation of trifluridine/tipiracil in a UK non-trial population. METHODS: Data collected routinely for the NPP were analysed to describe the patient demographics, clinical characteristics and treatment pathways. Patients eligible for the programme were adults (≥18 years) with histologically or cytologically confirmed mCRC who had previously received chemotherapy treatment(s). RESULTS: Of the 250 eligible patients enrolled in the NPP, 194 patients received ≥1 dose of trifluridine/tipiracil and 56 patients did not receive trifluridine/tipiracil. The following results are reported first for patients who received trifluridine/tipiracil and second for those who did not receive trifluridine/tipiracil: median (IQR) age was 63.0 (54.0-69.0) and 62.0 (54.8-69.0) years; Eastern Cooperative Oncology Group performance status score was 0 for 28 and 14%, 1 for 65 and 70%, 2 for 7 and 16%. In terms of previous systemic treatments 47 and 43% had 2 prior lines of therapy. FOLFOX-, FOLFIRI- and CAPOX-based therapies were the most common first-line regimens in patients receiving trifluridine/tipiracil (37, 35 and 21%, respectively), and in patients not receiving trifluridine/tipiracil (41, 30 and 20%, respectively). Second-line treatment regimens in patients receiving and not receiving trifluridine/tipiracil were most commonly FOLFIRI-based (48 and 41%, respectively) and FOLFOX-based (19 and 21%, respectively). Patients received a median of 2 cycles of trifluridine/tipiracil with a median treatment duration of 1.8 (95% CI: 1.8-2.4) months. In patients who discontinued treatment due to disease progression, the median progression-free duration was 2.8 (95% CI: 2.4-2.9) months. CONCLUSIONS: The results highlight the number of treatment pathways used to treat mCRC in routine UK clinical practice prior to the marketing authorisation and National Institute for Health and Care Excellence approval of trifluridine/tipiracil and highlight the lack of clinical guidelines for mCRC.

Biomimetic nanoparticles with enhanced affinity towards activated endothelium as versatile tools for theranostic drug delivery.

Activation of the vascular endothelium is characterized by increased expression of vascular adhesion molecules and chemokines. This activation occurs early in the progression of several diseases and triggers the recruitment of leukocytes. Inspired by the tropism of leukocytes, we investigated leukocyte-based biomimetic nanoparticles (i.e., leukosomes) as a novel theranostic platform for inflammatory diseases. Methods: Leukosomes were assembled by combining phospholipids and membrane proteins from leukocytes. For imaging applications, phospholipids modified with rhodamine and gadolinium were used. Leukosomes incubated with antibodies blocking lymphocyte function-associated antigen 1 (LFA-1) and CD45 were administered to explore their roles in targeting inflammation. In addition, relaxometric assessment of NPs was evaluated. Results: Liposomes and leukosomes were both spherical in shape with sizes ranging from 140-170 nm. Both NPs successfully integrated 8 and 13 µg of rhodamine and gadolinium, respectively, and demonstrated less than 4% variation in physicochemical features. Leukosomes demonstrated a 16-fold increase in breast tumor accumulation relative to liposomes. Furthermore, quantification of leukosomes in tumor vessels demonstrated a 4.5-fold increase in vessel lumens and a 14-fold increase in vessel walls. Investigating the targeting mechanism of action revealed that blockage of LFA-1 on leukosomes resulted in a 95% decrease in tumor accumulation. Whereas blockage of CD45 yielded a 60% decrease in targeting and significant increases in liver and spleen accumulation. In addition, when administered in mice with atherosclerotic plaques, leukosomes exhibited a 4-fold increase in the targeting of inflammatory vascular lesions. Lastly, relaxometric assessment of NPs demonstrated that the incorporation of membrane proteins into leukosomes did not impact the r1 and r2 relaxivities of the NPs, demonstrating 6 and 30 mM-1s-1, respectively. Conclusion: Our study demonstrates the ability of leukosomes to target activated vasculature and exhibit superior accumulation in tumors and vascular lesions. The versatility of the phospholipid backbone within leukosomes permits the incorporation of various contrast agents. Furthermore, leukosomes can potentially be loaded with therapeutics possessing diverse physical properties and thus warrant further investigation toward the development of powerful theranostic agents.

Preclinical characterization of tyrosine kinase inhibitor-based targeted therapies for neuroendocrine thyroid cancer.

Medullary thyroid carcinoma (MTC) is a slow growing neuroendocrine (NE) tumor for which few treatment options are available. Its incidence is rising and mortality rates have remained unchanged for decades. Increasing the repertoire of available treatments is thus crucial to manage MTC progression. Scarcity of patient samples and of relevant animal models are two challenges that have limited the development of effective non-surgical treatments. Here we use a clinically accurate mouse model of MTC to assess the effects and mode of action of the tyrosine kinase inhibitor (TKI) Vandetanib, one of only two drugs currently available to treat MTC. Effects on tumor progression, histopathology, and tumorigenic signaling were evaluated. Vandetanib blocked MTC growth through an anti-angiogenic mechanism. Furthermore, Vandetanib had an apparent anti-angiogenic effect in a patient MTC sample. Vandetanib displayed minimal anti-proliferative effects in vivo and in human and mouse MTC tumor-derived cells. Based on these results, we evaluated the second-generation TKI, Nintedanib, alone and in combination with the histone deacetylase (HDAC) inhibitor, Romidepsin, as potential alternative treatments to Vandetanib. Nintedanib showed an anti-angiogenic effect while Romidepsin decreased proliferation. Mechanistically, TKIs attenuated RET-, VEGFR2- and PI3K/AKT/FOXO signaling cascades. Nintedanib alone or in combination with Romidepsin, but not Vandetanib, inhibited mTOR signaling suggesting Nintedanib may have broader anti-cancer applicability. These findings validate the MTC mouse model as a clinically relevant platform for preclinical drug testing and reveal the modes of action and limitations of TKI therapies.

Complement and Cardiovascular Disease--The Missing Link in Haemodialysis Patients.

BACKGROUND: Patients on haemodialysis (HD) have high rates of cardiovascular (CV) disease and activation of the complement system. Despite evidence in non-renal patients that these may be linked, this association has received little attention in HD patients to date. In the setting of a randomised controlled trial we evaluated the relationships between baseline complement levels and subsequent CV events and mortality, in addition to the effects of HD with a vitamin E (VE)-coated dialysis membrane on circulating complement levels. METHODS: A total of 260 HD patients were randomised to dialysis with a VE-coated dialysis membrane or non-VE coated equivalent for 12 months. Blood samples were taken at baseline, 6 and 12 months for measurement of C3, factor D, factor H and SC5b-9 levels. Data were collected prospectively on deaths and CV events. RESULTS: Higher C3 levels at baseline were associated with subsequent CV events (hazard ratio 1.20 (1.01-1.42) per 0.1 mg/ml). Patients with intermediate SC5b-9 levels had significantly lower CV event rates and mortality than those with either high or low levels (p < 0.01). There were no effects of the VE-membranes on the complement components measured nor the clinical endpoints considered. CONCLUSIONS: The levels of C3 and SC5b-9 may have prognostic utility for predicting future CV events and/or mortality in HD patients - a relationship that requires further investigation. Dialysing prevalent HD patients with VE-bonded polysulfone membranes for a period of 12 months did not alter the circulating levels of the alternative complement pathway components considered here.

Genome-wide association study of L-arginine and dimethylarginines reveals novel metabolic pathway for symmetric dimethylarginine.

BACKGROUND: Dimethylarginines (DMA) interfere with nitric oxide formation by inhibiting nitric oxide synthase (asymmetrical DMA [ADMA]) and l-arginine uptake into the cell (ADMA and symmetrical DMA [SDMA]). In prospective clinical studies, ADMA has been characterized as a cardiovascular risk marker, whereas SDMA is a novel marker for renal function and associated with all-cause mortality after ischemic stroke. The aim of the current study was to characterize the environmental and genetic contributions to interindividual variability of these biomarkers. METHODS AND RESULTS: This study comprised a genome-wide association analysis of 3 well-characterized population-based cohorts (Framingham Heart Study [FHS; n=2992], Gutenberg Health Study [GHS; n=4354], and Multinational Monitoring of Trends and Determinants in Cardiovascular Disease Study [MONICA]/Cooperative Health Research in the Augsburg Area, Augsburg, Bavaria, Germany [KORA] F3 [n=581]) and identified replicated loci (DDAH1, MED23, Arg1, and AGXT2) associated with the interindividual variability in ADMA, l-arginine, and SDMA. Experimental in silico and in vitro studies confirmed functional significance of the identified AGXT2 variants. Clinical outcome analysis in 384 patients of the Leeds stroke study demonstrated an association between increased plasma levels of SDMA, AGXT2 variants, and various cardiometabolic risk factors. AGXT2 variants were not associated with poststroke survival in the Leeds study or were they associated with incident stroke in the Cohorts for Heart and Aging Research in Genomic Epidemiology (CHARGE) consortium. CONCLUSIONS: These genome-wide association study support the importance of DDAH1 and MED23/Arg1 in regulating ADMA and l-arginine metabolism, respectively, and identify a novel regulatory renal pathway for SDMA by AGXT2. AGXT2 variants might explain part of the pathogenic link between SDMA, renal function, and outcome. An association between AGXT2 variants and stroke is unclear and warrants further investigation.

Regulated localization is sufficient for hormonal control of regulator of G protein signaling homology Rho guanine nucleotide exchange factors (RH-RhoGEFs).

The regulator of G protein signaling homology (RH) Rho guanine nucleotide exchange factors (RhoGEFs) (p115RhoGEF, leukemia-associated RhoGEF, and PDZ-RhoGEF) contain an RH domain and are specific GEFs for the monomeric GTPase RhoA. The RH domains interact specifically with the α subunits of G12 heterotrimeric GTPases. Activated Gα13 modestly stimulates the exchange activity of both p115RhoGEF and leukemia-associated RhoGEF but not PDZ-RhoGEF. Because all three RH-RhoGEFs can localize to the plasma membrane upon expression of activated Gα13, cellular localization of these RhoGEFs has been proposed as a mechanism for controlling their activity. We use a small molecule-regulated heterodimerization system to rapidly control the localization of RH-RhoGEFs. Acute localization of the proteins to the plasma membrane activates RhoA within minutes and to levels that are comparable with activation of RhoA by hormonal stimulation of G protein-coupled receptors. The catalytic activity of membrane-localized RhoGEFs is not dependent on activated Gα13. We further show that the conserved RH domains can rewire two different RacGEFs to activate Rac1 in response to a traditional activator of RhoA. Thus, RH domains act as independent detectors for activated Gα13 and are sufficient to modulate the activity of RhoGEFs by hormones via mediating their localization to substrate, membrane-associated RhoA.

Genome-wide association study for circulating tissue plasminogen activator levels and functional follow-up implicates endothelial STXBP5 and STX2.

OBJECTIVE: Tissue plasminogen activator (tPA), a serine protease, catalyzes the conversion of plasminogen to plasmin, the major enzyme responsible for endogenous fibrinolysis. In some populations, elevated plasma levels of tPA have been associated with myocardial infarction and other cardiovascular diseases. We conducted a meta-analysis of genome-wide association studies to identify novel correlates of circulating levels of tPA. APPROACH AND RESULTS: Fourteen cohort studies with tPA measures (N=26 929) contributed to the meta-analysis. Three loci were significantly associated with circulating tPA levels (P<5.0×10(-8)). The first locus is on 6q24.3, with the lead single nucleotide polymorphism (SNP; rs9399599; P=2.9×10(-14)) within STXBP5. The second locus is on 8p11.21. The lead SNP (rs3136739; P=1.3×10(-9)) is intronic to POLB and <200 kb away from the tPA encoding the gene PLAT. We identified a nonsynonymous SNP (rs2020921) in modest linkage disequilibrium with rs3136739 (r(2)=0.50) within exon 5 of PLAT (P=2.0×10(-8)). The third locus is on 12q24.33, with the lead SNP (rs7301826; P=1.0×10(-9)) within intron 7 of STX2. We further found evidence for the association of lead SNPs in STXBP5 and STX2 with expression levels of the respective transcripts. In in vitro cell studies, silencing STXBP5 decreased the release of tPA from vascular endothelial cells, whereas silencing STX2 increased the tPA release. Through an in silico lookup, we found no associations of the 3 lead SNPs with coronary artery disease or stroke. CONCLUSIONS: We identified 3 loci associated with circulating tPA levels, the PLAT region, STXBP5, and STX2. Our functional studies implicate a novel role for STXBP5 and STX2 in regulating tPA release.